Abstract

Much has been written concerning the relationship between body size and biological traits, mostly concerning the terrestrial situation. There is no reason to suppose that many of these relationships will be different in the sea; for example quarter-power scaling with body mass applies to virtually all organisms (West, Brown & Enquist, 1999). For marine animals, metabolic rate and production scales at three-quarters power (e.g. Brey, 1990; Warwick & Price, 1979), while it is likely that life span increases in proportion to body mass raised to the power of one quarter, although so little is known about the natural history of marine animals that this latter relationship cannot yet be established. On the other hand, the very different phyletic composition of terrestrial and marine faunas, and the big differences in life-history characteristics, suggest that relationships between body size and diversity will differ between these two realms.

The relationship between body size and diversity is fraught with uncertainties and inconsistencies. Hutchinson (1959) suggested that ‘… small size, by permitting animals to become specialised to the conditions offered by small diversified elements of the environmental mosaic, clearly makes possible a degree of diversity quite unknown among groups of larger organisms’. However, it is now suggested that the spatial and temporal structure of the physical environment is fractal (Bell et al., 1993 and references therein; see Schmid & Schmid-Araya, this volume), and if habitat complexity largely determines species diversity this leads to the prediction (for a single perfect fractal) that all organisms, regardless of size, will perceive the environment as equally complex and should have equivalent diversity.